// Pure mapping helpers for the time-scale slider (v0.9.2) — no game logic, unit-testable
// in node. The slider has 7 discrete positions on a power-of-two ladder:
// 1× → 2× → 4× → 8× → 16× → 32× → 64×, so each step doubles the speed (matching
// POST /api/sim's clamp range [1, 64]).

export const TIME_SCALES = [1, 2, 4, 8, 16, 32, 64] as const;
export const MIN_SCALE: number = TIME_SCALES[0];
export const MAX_SCALE: number = TIME_SCALES[TIME_SCALES.length - 1];

const clamp = (v: number, lo: number, hi: number) => Math.min(hi, Math.max(lo, v));

// t → scale: the position maps to the nearest ladder step. Exact at the endpoints:
// sliderToScale(0) === 1, sliderToScale(1) === 64.
export function sliderToScale(t: number): number {
  const tt = clamp(Number.isFinite(t) ? t : 0, 0, 1);
  return TIME_SCALES[clamp(Math.round(tt * (TIME_SCALES.length - 1)), 0, TIME_SCALES.length - 1)];
}

// scale → t: the nearest ladder position by log2 distance. Exact at the endpoints:
// scaleToSlider(1) === 0, scaleToSlider(64) === 1; round-trips every value in TIME_SCALES.
export function scaleToSlider(scale: number): number {
  const s = clamp(Number.isFinite(scale) ? scale : MIN_SCALE, MIN_SCALE, MAX_SCALE);
  return Math.log2(s) / Math.log2(MAX_SCALE);
}